The Obama administration was on Friday on the verge of lifting protection for grey wolves across most of the country, ending a 20-year effort to bring the animals back to their historic range.

The move would withdraw protection in all lower 48 states for an iconic animal which is seen by its defenders as a symbol of the wide open spaces of the Rocky Mountain West – and by cattle ranchers as a plague on their herds. Only a small population of about 75 Mexican gray wolves, in Arizona and New Mexico, would remain under federal government protection, according to the Los Angeles Times, which obtained a draft of the rule.

The US Fish and Wildlife Service told reporters the new rule was still under review, and would be open for public comment.

The latest moves, as revealed in the draft, would leave it up to individual states to manage wolf populations. Conservationists said that could undermine wolves’ recovery in large parts of the Rockies. Officials reasoned that the recovery of the population in the Rocky Mountain states, where there are an estimated 1,600 wolves, and scattered populations in California, Oregon, Washington and parts of New England meant the animals were assured of survival across large parts of the country. However, wildlife biologists argued ending protections for wolves risked undoing a rare conservation success story.

Since their re-introduction in the 1990s, with about 60 animals brought in from Canada, wolf populations have rebounded in the Rocky Mountain West. The animals were prolific breeders and they also roamed widely, re-establishing populations across large swathes of the Rockies.

But there was a strong backlash against their recovery from ranchers, who faced attacks on their livestock, and from hunters, who said the animals were taking too big a toll on elk populations.